*) Fix user defined type stuff

*) Implement top level stuff

*) Rewrite type checker to collect and then solve constraints

*) Extend it to allow for referencing declarations "further down" in file, but make sure it
terminates by forbidding corecursion (simply done by building a reference graph and then looking at it)

*) Add Kind env and type parameters

*) Type annotated tree?

*) Make SECD machine good enough to execute it

*) Write backend for SECD machine code

*) Pattern matching to recursor syntactic sugar

*) Record types